Pavement materials, such as soil, sand, aggregate, asphalt, and cement, require quality testing for qualities such as moisture and density. Destructive tests and nondestructive tests are used throughout the industry for determining these qualities. In laboratory destructive tests, cylindrical samples are prepared, typically with a gyratory compactor, and various material properties are studied to determine the best mix design for a pavement. In field destructive tests, cylindrical samples are cored from test strips, newly constructed roads, or existing roads. The material properties of these samples are then used to evaluate whether the test strip or the new pavement meets the design criteria and whether the existing road is in good operating condition or in need of repairs. Currently, several methods are used for measuring the density of cylindrical samples: dimensional analysis, the water displacement method, the paraffin coated method, the vacuum sealed method, and the para-film-covered method. In each case, the bulk density of a sample is derived by, as in the definition, dividing the dry sample mass by the estimated sample volume. All methods require a balance with a sensitivity of 0.1 gram (g) to measure the mass of the sample. In the dimensional analysis method, sample volume is determined from the radius and thickness (height) measurements. In this example, many readings of the radius and thickness of the sample are made using either manually a Vernier caliper or automatically using a laser system. The average values of the radius and the thickness are then used to calculate the sample volume. This method overestimates the volume thus underestimating the density as it does not fully account for the surface features of the aggregate mix boundary.
Other methods use the Archimedes Principle for determining the sample volume. These methods require a large container filled with clean water. The water temperature may be monitored and controlled at a specific temperature, e.g. at 25° C. At one stage of the test, the sample is kept immersed in water for approximately 4 minutes and the weight of the sample, while suspended in water, is recorded. In the “paraffin-coated” method, after determining the dry weight of the sample, a thin coating of paraffin is applied to cover the entire surface area of the sample. Then, the sample is weighed again in air. Finally, the sample is weighed while immersed in water. More details can be found in standards ASTM D 2726 for the water displacement method and ASTM D 1188 for the paraffin-coated method.
Nondestructive field measurements of asphalt are typically accomplished with nuclear gauges. Nuclear radiation gauges have been widely used for measuring the density of soil and asphaltic materials. Such gauges typically include a source of gamma radiation which directs gamma radiation into the test material, and a radiation detector located adjacent to the surface of the test material for detecting radiation scattered back to the surface. From this detector reading, a determination of the density of the material can be made. Nuclear gauges, however, require a high degree of training and radiological management for the operators of these gauges. Therefore, it would be desirable to obtain accurate field measurement gauges without the use of nuclear gauges.